The present invention relates to a method and a device for the conversion of organic materials into gaseous or liquid fuels and in particular relates to the use of flash pyrolytic conversion of organic materials into gaseous or liquid fuels.
The conversion of organic waste into fuel by means of flash pyrolysis is a relatively new area of technology. There has, however, been some development in the general area of pyrolytic conversion of organic waste. One of the former methods of pyrolytic conversion for the production of gaseous fuels suggests loading waste organic materials into the top of a shaft furnace which is provided with an oxygen inlet at its lower end. Subsequent pyrolysis of the organic waste results in the formation of molten slag in the bottom of the furnace and a product gas comprising a fuel gas, oil, water vapor and fly ash. The product gas exits from the top of the furnace. The oil and the fly ash are removed from the product gas and recycled back to the furnace. The water vapor is subsequently removed in a condenser. Unfortunately, the resultant fuel gas has a heating value of only one-third of natural gas.
Another former method of pyrolytic conversion of organic waste involves low temperature pyrolysis. The organic waste is fed into the top of a vertical reactor where it is progressively dried, charred and finally oxidized at a relatively low temperature. These transformations occur while the organic material is settling under the force of gravity. The product gas which is formed at the lower end of the reactor rises, dries and chars the incoming organic waste. The resultant product gas leaving the reactor contains hydrogen, oxides of carbon, water vapor and a mixture of hydrocarbons. Since the product gas contains no ashy material, it may be cleanly burned in a secondary burner. The product gas may also be further processed to yield a gaseous mixture, containing hydrogen and carbon monoxide, which can then be used to synthesize methane.
Another former method of pyrolytic conversion of organic material into a fuel product involves high pressure, low temperature pyrolysis. The organic material is pulverized, mixed with water and pumped as a slurry into a reactor containing under pressure a carbon monoxide atmosphere or other suitable atmosphere. The organic material is subsequently pyrolized to produce an oil product. Residence time within the reactor is approximately 20 - 30 minutes. The resultant product oil is forced to the top of the reactor by incoming organic material and exits the reactor into appropriate separation equipment for removal of water vapor, ashe and carboneous char. The synthetic oil produced is a mixture of complex hydrocarbons.
Another former method utilizes a two reactor system to prevent the introduction of oxygen into the pyrolytic reactor. In this system the organic material is fed into the pyrolytic reactor which contains a heated fluidized sand/char bed. The organic material is subsequently pyrolized by the sand/char mixture to produce a fuel product. The sand/char mixture is removed from the reactor into a separate vessel for heating and recycled through connecting duct back to the pyrolytic reactor. The sand/char mixture thus provides the heat necessary for pyrolysis.
The above described methods of converting organic material into fuel have not been completely economical or technically viable. In the first three methods described, the product gas produced has a low heating value, ranging from approximately 350 - 550 Btu/Scf. This is due to the fact that the product gas contains a relatively large percentage of combustion gases such as carbon dioxide and nitrogen. Therefore, the product gas is not acceptable for gas pipeline application or as a substitute for natural gas. The last method described is for the production of a synthetic oil in a non-oxidizing atmosphere. This system does not appear to be economically or technically viable due to clogging, coke and sludge formation within the reactor and the excessive amount of heat required to vaporize the slurry mixture. The coke and sludge buildup occur inside the reactor and are caused by the conversion of the organic material into hard carbon or coke. The coke buildup and sludge formation prohibit efficient operation of the reactor and result in a reduction of heat transfer through the walls of the vessel. This reduction in heat transfer eventually results in a burn-through of the vessel walls which necessitates a shutdown of the reactor for repairs. Clogging occurs when a chunk of coke breaks off from the wall of the vessel and moves through the reactor until it encounters a restriction. Clogging will also eventually necessitate a shutdown of the reactor for repairs.